Many systems have been developed for applying liquid herbicides to weeds. Aside from spraying, most herbicide applicators employ a contact applicator head or wiper bar designed to be saturated with herbicide liquid and wiped over the weeds. Herbicide is thereby transferred from the surface of the applicator to the weeds. Contact herbicide applicators have come to be generally preferred over spray applicators in certain situations, in particular to apply non-selective herbicides such as ROUNDUP to weeds growing among desirable vegetation. However, such herbicides are expensive. Therefore, an important concern is to minimize waste. Controlling dripping is also important to protect desirable plants.
Hand-held contact herbicide applicators are primarily used for lawns and gardens. Some applicator designs simply provide handles with an absorbent head or mop which is dipped into a container of herbicide. Another common design is a hockey-stick shaped tool which uses an internal gravity feed system with the flow rate to the wiper or wicking head regulated by an operator-controlled valve.
For example, U.S. Pat. Nos. 4,291,491, 4,305,224, and 4,357,779 to Maddock generally disclose applicators having a vented storage chamber at the top of the handle for herbicide liquid and a drip valve in the handle for metering a predetermined amount of fluid down the handle to a wicking head. The operator must adjust the valve setting to match herbicide flow to the rate at which weeds are wiped. Too much flow and the wicking head drips and wastes herbicide. Too little, and not enough herbicide, is wiped on the weeds. Hence, frequent operator adjustment is required.
Other hand-held contact applicators are known, such as U.S. Pat. No. 4,409,755 to Maddock, which use the entire handle as the reservoir for the liquid. An orifice is provided at a joint between the wicking head and the handle for metering herbicide liquid into the wicking head. The foregoing forms of applicators ordinarily tend to supply too much liquid to the wicking head, resulting in leakage and waste of the expensive herbicide liquid and damage to desired plants.
Another hand-held herbicide applicator designed particularly for spot-applying herbicide by direct contact with woody-type vegetation is disclosed in U.S. Pat. No. 4,027,986 to Patrick. That applicator uses a hollow handle for storage of herbicide liquid and a partial vacuum is maintained at the top of the handle. An operator-controlled air-bleed valve at the top end of the handle is actuated to bleed air into the handle to regulate an otherwise free flow of liquid into the applicator head. While this system enables better control of the flow of herbicide liquid to the wicking head, it still requires the operator to adjust a valve often to assure an adequate yet not excessive supply of liquid herbicide.
U.S. Pat. No. 4,403,881 to Keeton uses an upper portion of the handle to store herbicide liquid above a diaphragm with a small slit extending through it. A manual pump mechanism is provided at the top of the handle to expel a small amount of liquid at a time through the slit. This design also requires frequent action by the operator to provide an adequate amount of liquid to the applicator head.
U.S. Pat. No. 4,369,596 to Hartford discloses a contact herbicide applicator for mounting on the back of a lawnmower. Hartford uses a feed arrangement for supplying herbicide liquid from an elevated tank under a partial vacuum to a large-diameter tube which is partially filled to serve as a wiper bar. The herbicide liquid is dispensed into a surrounding wicking material through a plurality of holes in rows extending horizontally along the opposite sides of the wiper bar. Such an apparatus appears to alleviate the need for manual control but continuously feeds liquid herbicide to the wiper bar and therefore would likely drip when not actually wiping. Also, anytime the wiper bar is tilted from horizontal, the supply of liquid to the wicking material would be uneven and dispensing of liquid from the tank would either cease or increase depending on the direction of tilt.
For agricultural field use, U.S. Pat. No. 4,332,107 to Reed discloses a multi-layer applicator wiper bar mounted on the front end of a tractor. Herbicide liquid is gravity-fed to surrounding wicking material through rows of holes extending along the wiper bar. The flow of liquid herbicide is regulated by adjusting the liquid pressure or head at the wiper bar by raising or lowering a tank of liquid herbicide carried on the tractor. Like the hand-held applicators, this system also requires constant monitoring by the operator to assure an adequate yet not excessive flow of herbicide liquid to the wiper bar. A commercially-available wiper bar similar to Reed's is the Weed Wiper Super-7 TM offered by Century Engineering, P.O. Box 3018, Cedar Rapids, Iowa 52406. Flow of liquid herbicide from a reservoir tank to the wiper bar is controlled by an operator-actuated solenoid valve. Excess liquid flow easily occurs with this system, which wastes herbicide and could damage the crops. This wiper bar, as well as those disclosed above requires constant operator supervision for proper herbicide feed rates.